This invention relates to a pump intended for high pressure pumping and delivery of almost any liquid such as water, petrol, gas oil, oils, corrosive chemical liquids and sludge, but more particularly for the high pressure supply of fuel injectors for internal combustion engines.
Low pressure pumps are known for liquids of this type, and are generally centrifugal pumps, gear pumps, sometimes piston pumps or other types of pumps. With these known pumps, a high delivery pressure (in excess of 50 bars) either cannot be obtained or only with great difficulty and at great expense due to the fact that, once one starts using high pressures, the moving parts begin to seize and substantial leaking occurs due to the often very low viscosity of the liquids pumped.
To avoid such seizure or leakage, diaphragm pumps have been known to be used, in which case it becomes impossible to achieve high delivery pressure. In fact, the diaphragm is driven by a mechanical means (cam, lever or the like) on one side, and is subjected on the other side to the delivery pressure: it ensures that, once the pressure becomes high, the diaphragm deteriorates at the points where mechanical stress is applied.
Also known, to pump special liquids such as corrosive liquids, is the association of two pumps: a first pump which is a hydraulic pump that delivers and draws back a hydraulic liquid which, by way of reciprocating motion, drives the mobile elements of a second pump which draws in and pressurizes the liquid to be pumped. These mobile elements which ensure physical separation of the hydraulic liquid and the liquid to be pumped, though driven in reciprocating motion by the hydraulic liquid, are either deformable diaphragms or free-floating pistons.
The free-floating pistons are defective from the point of view of tightness, and this defect cannot be overcome when absolute tightness is required. If a seal is fitted between the free-floating piston and the cylinder in which it moves, perfect tightness cannot be obtained. If the seal is eliminated, either there will be a very thin film of oil between the friction surfaces and therefore micro-leakage, or the rubbing surfaces will heat up if there is no film of oil. In the particular case of high pressure fuel injection, no leakage, no matter how small, can be tolerated and, of course, heating is liable to cause an explosion.
The known free-floating piston-type devices, such as e.g., U.S. Pat. No. 4,443,160, must therefore be ruled out.
The invention thus relates to a pumping device in which the mobile elements--to which a reciprocating pumping motion is imparted by the hydraulic pump and which ensure a perfectly tight separation between the hydraulic "driving" liquid and the liquid to be pumped--are deformable diaphragms.
Generally, this type of deformable diaphragm pump has at least one of the following drawbacks and sometimes several simultaneously:
a--if the separating and pumping diaphragm is mechanically linked to the piston of the hydraulic pump, there is not equal pressure on both sides of the flexible diaphragm as a result of which the latter will not last over time, it will deteriorate; PA1 b--if the diaphragm is completely free, i.e., unattached to any drive mechanism and driven solely by the hydraulic liquid delivered by the pump, there will be equality of pressure on the two sides of the diaphragm. However, due to inevitable leaks, even very minute ones, the volume of hydraulic liquid delivered increases with each cycle and ultimately exceeds the volume the diaphragm can deliver; this causes a hydraulic blocking which creates so much excess pressure that one or other of the pumps breaks. In the particular case of high pressure fuel injection, if the element that breaks is the element delivering the fuel, fire will inevitably break out, PA1 c--in both eases, i.e., whether the diaphragm is attached to the piston or unattached, if the volume of hydraulic liquid continually being drawn in and delivered is constantly the same, the diaphragm will heat up as a result of the indefinitely repeated compression cycles, until it reaches a temperature such that the diaphragm(s) break. PA1 a--the second pump comprises as many volumes or bores as the first pump has bores, each bore of the second pump communicating directly with the corresponding bore of the first pump so that each piston of the first pump cyclically delivers and draws the hydraulic liquid into the corresponding bore of the second pump; PA1 b--each bore of the second pump is divided into two parts by a deformable diaphragm held in countercheck by a spring, the part communicating with the corresponding bore of the first pump receiving the hydraulic liquid delivered and drawn back by the first pump, and the other part, which is fitted with suction and delivery valves, performing suction and delivery of the product to be pumped; PA1 c--the chamber in which the piston heads move back and forth is connected to a reservoir of hydraulic liquid; PA1 d--the reservoir of hydraulic liquid is on the exterior of the first pump and communicates with the latter by means of a pipe leading into the chamber; PA1 e--the pump embodying the invention is destined for the high pressure supply of fuel injectors for internal combustion engines, and the hydraulic liquid of the first pump (I) can be the oil of the engine. PA1 a--the pistons slide in two support members drilled with orifices, the two support members being separated from one another by an annular space, constituting a chamber, in which the liners moved between two extreme positions: in one of these positions, as the orifices are not obstructed by the liner, all the liquid delivered by each piston flows back into the annular chamber via the orifices of the piston as the pump (I) rate is zero; in the other of these positions, as all the orifices are covered by the liners, each piston forces back all the hydraulic liquid drawn in, the flow rate of the pump then being at maximum. PA1 b--the liners can be in all intermediate positions included between the two extreme positions, as a result of which the flow rate of the pump (I) can be set at all values included between zero and the maximum rate. PA1 c--the liners are coupled to a common control unit which is driven by any control device appropriate for the regulation of the high pressure flow of fuel as a function of the engine supply requirements without any reflux of high pressure fuel to the reservoir. PA1 d--a damping device can be located downstream of the outlet of the second pump (II) and upstream of the injectors to cancel the pulsation effect brought about by the first pump (I). PA1 e--the damping device can be a capacity of sizable volume in relation to the fuel rate, maintained at the injection pressure by any appropriate means and can behave substantially in the manner of a hydromechanical accumulator.
U.S. Pat. No. 4,392,787 granted to Notta discloses a unit including a hydraulic slanted plant pump, each piston of the pump being associated at its end with a flexible diaphragm which is connected to a rod that slides inside the piston. This device has the drawbacks described above in "a" and "c". The volume of liquid continually pressurized is always the same and will therefore heat up. Moreover, the inevitable little leaks are offset by the intake of additional oil via a non-return valve, but should a substantial leak accidentally occur, the piston will come into mechanical contact with the diaphragm thus destroying the latter.
U.S. Pat. No. 2,960,936 granted to Dean describes a pump in which a completely unattached diaphragm is cyclically pressed and released by a hydraulic volume displaced by a cam-driven piston. This device has drawbacks "b" and "c". If, for any reason, the supply were to be stopped or slowed down, the diaphragm would not completely redeploy itself and a corresponding quantity of hydraulic liquid would be introduced at each cycle until the occurrence of breakage (drawback "b"). Furthermore, as the volume of hydraulic liquid compressed is always the same, heating will inevitably take place (drawback "c").
German Patent No. 2,447,741 granted to Wanner discloses a diaphragm pump mechanically linked to a piston which slides inside a hydraulic pump piston. The drawbacks are the same as for above-mentioned U.S. Pat. No. 4,392,787.